1. Field of the Invention
The present invention relates to a surface light source device, a method of manufacturing the surface light source device and a back light unit having the surface light source device. More particularly, the present invention relates to a surface light source device having a stripe shaped discharge space, a method of manufacturing the surface light source device and a back light unit having the surface light source device as a light source.
2. Description of the Related Art
Generally, liquid crystal (LC) has a specific electrical and optical characteristic.
In detail, when electric fields that are applied to the LC are changed, an arrangement of the LC molecules is also changed. As a result, an optical transmittance is changed.
A liquid crystal display (LCD) apparatus uses the above-explained characters of LC to display an image. The LCD apparatus has many merits, for example such as a small volume, a lightweight, etc. Therefore, LCD apparatus is used in various fields, for example such as a notebook computer, a mobile phone, television set, etc.
The LCD apparatus includes a liquid crystal controlling part and a light providing part. The liquid crystal controlling part controls the LC. The light providing part provides the liquid crystal controlling part with a light.
The liquid crystal controlling part includes a pixel electrode formed on a first substrate, a common electrode formed on a second substrate and a liquid crystal layer interposed between the pixel electrode and the common electrode. A number of the pixel electrode is determined in accordance with resolution, and a number of the common electrode is one. Each of the pixel electrodes is electrically connected to a thin film transistor (TFT), so that a pixel voltage is applied to the pixel electrode through the TFT. A reference voltage is applied to the common electrode. Both of the pixel electrode and common electrode include an electrically conductive and optically transparent material.
The light providing part provides the liquid crystal controlling part with a light. The light generated from the light providing part passes through the pixel electrode, the liquid crystal layer and the common electrode in sequence. Therefore, luminance and uniformity of the luminance have great influence on a display quality of the LCD apparatus.
A conventional light providing part employs a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED). The CCFL has a long cylindrical shape, and the LED has a small dot shape.
The CCFL has a high luminance and a long lifespan, and generates small amount of heat. The LED has low power consumption and a high luminance. However, both the CCFL and LED have a low uniformity of luminance.
Therefore, in order to enhance the uniformity of luminance, the light providing part requires optical members such as a light guide plate (LGP), a diffusion member, a prism sheet, etc. Therefore, a volume and a weight of the LCD apparatus increase.
In order to solve above-mentioned problem, a surface light source device has been developed. A conventional surface light source device includes a first and second substrates spaced apart from each other, and a plurality of partition walls interposed between the first and second substrate. The partition walls are arranged in parallel with each other to define a plurality of discharge spaces. A sealing member is interposed between the first and second substrates to combine the first and second substrates. Discharge gas is injected into the discharge space. Electrodes for applying voltage to the discharge gas are formed at edge portion of the first and second substrates.
In order to maintain a pressure of the discharge spaces, the discharge spaces are connected to each other. For example, the partition walls are disposed alternately, so that the discharge spaces form a serpentine shape. Alternatively, a portion of the partition walls may be cut or holes may be formed at the partition walls to connect the discharge space with each other. Therefore, the discharge gas is distributed uniformly.
In order to define the discharge spaces, one of the first and second substrates may be transformed to form a partition wall that is integrally formed with the one of the first and second substrates (hereinafter, referred to as “substrate transforming method”). Alternatively, a partition wall that is separately formed with the first and second substrates may be interposed between the first and second substrates to define the discharge space between the first and second substrates (hereinafter, referred to as “partition inserting method”).
According to the substrate transforming method, a glass substrate is heated and compressed by mold, so that the glass substrate is transformed to have a plurality of furrows. The transformed glass substrate is combined with other glass substrate by frit. A space between the furrows corresponds to the discharge space, and the furrows correspond to the partition walls.
According to the partition inserting method, a partition wall including glass or ceramic is formed on a glass substrate, and other glass substrate is combined with the partition wall. Therefore, a space defined by the glass substrates and the partition wall corresponds to the discharge space.
FIG. 1 is a partially cutout perspective view illustrating a conventional surface light source device.
Referring to FIG. 1, a conventional surface light source device 100 includes a light source body 110, a plurality of partition walls 120 and a voltage applying part 130. The light source body 110 includes a first substrate 112, a second substrate 114 and a sealing member 116. The sealing member 116 is disposed along edge portion of the first and second substrates 112 and 114. The partition walls 120 are disposed between the first and second substrates 112 and 114 such that the partition walls 120 are parallel with each other. The spaces between the partition walls 120 are defined as the discharge space.
First end of odd numbered partition walls makes contact with the sealing member 116, and second end of the even numbered partition walls makes contact with the sealing member 116. Therefore, the discharge spaces defined by the partition walls 120 are connected to each other and have a serpentine shape.
Therefore, discharge gas injected into the discharge space spreads uniformly, and the discharge spaces have same pressure.
The light source body 110 includes a fluorescent layer formed on a surface of the first and second substrates 112 and 114, and the partition walls 120.
The voltage applying part 130 includes two electrodes 130a and 130b. The electrodes 130a and 130b are disposed at opposite end of the light source body 110, such that a longitudinal direction of the electrodes 130a and 130b is substantially perpendicular with a longitudinal direction of the partition wall 120. A conductive tape may be employed as the electrodes 130a and 130b. 
When discharge voltages are applied to the electrodes 130a and 130b, discharge gas disposed in the discharge space generates ultraviolet light. The ultraviolet light generated from the discharge gas is converted into a visible light by the fluorescent layer.
However, according to the conventional surface light source device of which discharge spaces having serpentine shape, plasma is concentrated in one of the discharge space due to minute difference. Then, the difference becomes more serious. The above-mentioned effect is referred to as “current drift effect”, “cross talk effect” or “channeling effect”. The above-mentioned current drift effect is observed even the conventional surface light source device having partition wall or partition walls having connection hole that connects the discharge spaces.
The current drift effect lowers the uniformity of luminance. Therefore, when an LCD apparatus employs the conventional surface light source device, a display quality is deteriorated.